Sheet-fed stamping presses, especially such stamping presses that are adapted to carry out hot-stamping of foil material are known in the art, for instance from International (PCT) Publications Nos. WO 97/35721 A1, WO 97/35794 A1, WO 97/35795 A1, WO 97/36756 A1, WO 03/043823 A1, WO 2005/102733 A2 and WO 2008/104904 A1, which publications are incorporated herein by reference in their entirety.
FIG. 1 is an illustration of a known sheet-fed stamping press, designated globally by reference numeral 10, as discussed in the aforementioned publications. This sheet-fed stamping press 10 is designed for performing hot-stamping of foil material onto successive sheets S which are fed from a sheet feeder 1 supplying individual sheets S in succession from a sheet feeding pile 15 for processing in a downstream-located foil application unit 2. This foil application unit 2 is designed in the present illustration to allow transfer by hot-stamping of foil material onto the successive sheets S, which foil material is conventionally fed to the foil application unit 2 in the form of a continuous band by means of a foil feeding system 3. More precisely, the foil material to be transferred onto the sheets S is provided on a suitable foil carrier FC, which is brought into contact with the surface of the sheets S so as to allow transfer of the foil material from the foil carrier FC onto the sheets S under the combined application of heat and pressure.
Alternatively, the foil application unit 2 could be adapted to allow lamination of foil material as for instance disclosed in International (PCT) Publication No. WO 2008/104904 A1 (see also International (PCT) Publications Nos. WO 2009/112989 A1 and WO 2010/001317 A1, which are likewise incorporated herein by reference in their entirety). In this case, at least a part of the foil carrier FC is laminated onto the sheets S as part of the applied foil material.
The foil application unit 2 comprises a heated stamping cylinder 21 with at least one, usually multiple circumferential stamping sections 210 (see FIG. 2) that are provided on a circumference of the stamping cylinder 21. In the illustrated example, one will appreciate that the stamping cylinder 21 actually comprises a plurality of (namely six) circumferential stamping sections 210 that are provided on the circumference of the stamping cylinder and distributed axially along an axis of rotation of the stamping cylinder 21 (i.e. along direction x in FIG. 2) at a plurality of axial positions, which axial positions correspond to different columns of security imprints that are present on the sheets S. Each circumferential stamping section 210 actually comprises successive stamping segments 211 that are distributed one after the other about the circumference of the stamping cylinder 21 (i.e. along the circumferential direction y in FIG. 2). In the illustrated example, the stamping cylinder 21 is a four-segment cylinder and each stamping section 210 accordingly comprises four such stamping segments 211, which are conventionally designed as individual stamping segments that are secured at both ends in corresponding cylinder pits 21b as discussed in greater detail in International (PCT) Publication No. WO 2005/102733 A2.
As shown in FIGS. 1 and 2, four sets of sheet holding units 21a are distributed about the circumference of the stamping cylinder 21 in order to hold a leading edge of each successive sheet S that is fed to the stamping cylinder 21. These sheet holding units 21a can in particular be configured as suction units that are designed to hold the leading edge of a sheet S by suction. In the illustrated example, the sheet holding units 21a are integrated into a number of bridge elements 215 that are provided and secured in the cylinder pits 21b as illustrated in FIG. 2 and discussed in greater detail in International (PCT) Publication No. WO 2005/102733 A2.
The foil carrier FC is typically fed to the foil application unit 2 by means of the foil feeding system 3 that comprises one or more supply rolls 31 for the supply of the foil carrier FC and one or more winding-up rolls 32 for winding up used foil carrier, designated by reference numeral FC*. The particular structure of the foil feeding system 3 is not of major relevance in the context of the instant invention. It suffices to understand that the foil feeding system 3 is adapted to supply the foil carrier FC in register with the sheets S. More detailed information regarding the structure and operation of the foil feeding system 3 can be found for instance in International (PCT) Publication No. WO 94/13487 A1, which is incorporated herein by reference in its entirety.
In the aforementioned stamping press, it will be understood that the foil carrier FC is fed from the foil feeding system 3 to the stamping cylinder 21 between the circumferential stamping sections 210 and the sheets S that are fed from the sheet feeder 1.
As illustrated in FIG. 1, multiple counter-pressure rollers 22 are provided about a portion of the circumference of the stamping cylinder 21. More precisely, the counter-pressure rollers 22 are arranged in pairs and distributed about a lower portion of the circumference of the stamping cylinder 21 (in the illustrated example, three such pairs of counter-pressure rollers 22 are provided as shown in FIG. 1) so as to press the underside of the sheet S against the circumference of the stamping cylinder 21 and thereby ensure application of a suitable pressure between the foil carrier FC and the sheet S to cause transfer of the foil material from its carrier FC onto the sheet S. This transfer is also ensured through the application of heat applied via the stamping cylinder 21 that is heated up to a suitable temperature. The pairs of counter-pressure rollers 22 are typically constructed as individual counter-pressure unit each comprising its own pneumatic (or hydraulic) cylinder or piston 23 designed to press the counter-pressure rollers 22 against the circumference of the stamping cylinder 21, or more exactly against the circumference of the circumferential stamping sections 210. European Patent Publication No. EP 0 582 178 A1 and International (PCT) Publication No. WO 2005/120832 A1, which are incorporated herein by reference in their entirety, disclose further details of counter-pressure roller systems for stamping presses.
In the aforementioned context, as illustrated in FIG. 2, each stamping segment 211 of the circumferential stamping sections 210 typically comprises corresponding stamping surface(s) 211a, which come into contact with the foil carrier FC, as well as supporting tracks 211b located on either side of the stamping surface(s) 211a, which come into contact with the sheets S, outside of the region where the foil carrier FC is present, so as to provide continuous support for the counter-pressure rollers 22. As shown in FIG. 2, the supporting tracks 211b are aligned with the bridge elements 215 so as to provide uninterrupted support for the counter-pressure rollers 22 across the region of the cylinder pits 21b. In the illustration of FIG. 2, each stamping segment 211 includes a plurality of individual stamping surfaces 211a, which is typical for the application of individual patches of foil material onto the sheets S. In the event of a stripe application, each stamping segment 211 would typically include a single, continuous stamping surface 211a to cause transfer of a corresponding continuous stripe of foil material onto the sheets S.
Downstream of the foil application unit 2, there is typically provided a conveyor system 4 for conveying the sheets S and foil carrier FC, which is still attached to the sheets S, away from the stamping cylinder 21. This conveyor system 4 conventionally comprises conveyor belts or bands 41 and a cooling roller 42 about the circumference of which the sheets S and foil carrier FC are brought in order to cool-down the sheets S and foil carrier FC and thereby enhance adhesion of the foil material onto the sheets S prior to separation of the foil carrier FC. A foil detachment device 45 is also typically provided along the path of the conveyor system 4 so as to separate the foil carrier FC from the sheets S. The used foil carrier FC* is then wound up around the winding-up roll(s) 32 or possibly fed again upstream of the foil application unit 2 (which is typically done in case of patch application—see again International (PCT) Publication No. WO 94/13487 A1).
At a downstream end of the conveyor system 4, there is typically provided a suction drum 46 that works in conjunction with a downstream-located chain-gripper system to transport and deliver the processed sheets, designated by reference numeral S* for the sake of distinction, in a sheet delivery unit 5 of the stamping press 10. More precisely, the chain-gripper system consists of chain wheels 51, 52 driving a pair of endless chains 53 extending therebetween and holding spaced-apart gripper bars 54 designed to hold the processed sheets S* by a leading edge thereof and transport the processed sheets S* individually in order to be delivered on top of a sheet delivery pile 55. More than one delivery pile 55 may be provided.
A problem with the aforementioned sheet-fed stamping press resides in the fact that the counter-pressure rollers 22, which are pressed against the underside of the sheets S exert a braking force on the sheets S, which braking force may cause undesired movement or slippage of the sheets S with respect to the circumference of the stamping cylinder 21. Such movement or slippage of the sheets S in turn causes stress on the foil carrier FC and/or affects a proper register of the foil material with respect to the sheets S, which is not desired.
There is therefore a need to improve the known sheet-fed stamping presses.